The goal of the Mouse Imaging Core is to develop and apply methods for intravital imaging of apoptosis and mitosis at the single cell level to tumors created by human xenografts, oncogene expression and serial passage of transplanted syngeneic cancer cells. The ability to monitor the molecular and pathophysiological features of tumors is critical for translating discoveries made in cell lines, which constitute the majority of the work in this program project, to actual cancers growing in situ. The mouse imaging core will develop cell lines and transgenic mice expressing tagged fluorescent proteins that serve as morphological and activitybased reporters of mitotic and apoptotic state. Because only a limited number of fluorescence channels (2-4) can be monitored simultaneously in live-cell experiments, no single cell line or mouse will be suitable for all of the proposed studies. Thus, several sets of compatible probes will be developed to monitor different aspects of mitosis and apoptosis in situ; experiments involving complementary reporter combinafions will then be combined. Typically these will involve intravital imaging through windows implanted in the skin or mammary glands. Animals carrying labeled tumors will then be exposed to various combinations of drugs and tumor responses then monitored over time at single-cell resolution. The core will undertake the development of quantitafive methods for immune-fluorescence analysis of fixed whole-mount and sectioned tumors. This work will build on extensive experience in the participafing laboratories with automated image analysis in cultured cells. Finally, the Core will provide access to a range of whole-body imaging methods developed for non-invasive determinafion of tumor morphology and size. Raw images and the results of image analysis will be distributed to all investigators in the Program using a web portal. Core activities will be divided between Massachusettes General Hospital (MGH) where the imaging equipment and Core Director Ralph Weissleder are based, and Harvard Medical School (MGH) where the experimental projects and Core co-Director Sorger are based. Imaging will be performed at MGH whereas mouse colonies will be generated and maintained at HMS. Preliminary studies have demonstrated this arrangement to be highly effective.